Thermo-Mechanical Design of Canapu PIP System

This paper discusses the thermo-mechanical design of the pipe-in-pipe (PIP) flowline installed in the Canapu field, located in Espi´rito Santo State, offshore Brazil. The pipeline is approximately 20km in length and connects the gas producing well 4-ESS-138 positioned in a depth of 1608m to Cidade de Vito´ria FPSO, located in Golfinho field. The Canapu PIP will operate under high pressure and temperature (HP/HT) conditions and is laid on the seabed. Due to the operational conditions, the thermo-mechanical design evaluated the susceptibility of the pipeline to the phenomenon of lateral buckling and pipeline walking in addition to free spanning and on-bottom stability. The lateral buckling behavior of the PIP is the major challenge for the design. It can be a safe and effective way to accommodate the thermal expansion of a hot pipeline, however high stress and strains can be developed in the buckles and a conventional stress based approach is not suited to design a pipeline that buckles laterally. The conventional stress limits are therefore relaxed and replaced by a strain limit. For this the methodology and recommendations of the SAFEBUCK JIP were adopted. The thermo-mechanical analysis selected a buckle initiation strategy based on distributed buoyancy. The strategy combines three distributed buoyancy triggers along the route together with the beneficial effect of the bathymetric out-of-straightness. The analysis shows that this initiation strategy is robust and highly reliable. From the start, this project represented a great challenge for Petrobras; it is the first PIP in Petrobras; has a low value specified for OHTC; and the pipeline is susceptible to lateral buckling. Besides all that, since the Canapu project was included among the priorities of Petrobras Plangas, it was executed as a fast track project.